Filtering units for filtering fluid, such as oil, are known in the art. A filter unit is typically placed in the oil line of an internal combustion engine to remove particulate matters and other contaminants from the oil to provide longer engine life and improved engine performance.
One typical oil filter unit has a cylindrical canister or housing which encloses a tubular filter element. One end of the canister is adapted for coupling to the engine block of the internal combustion engine. A typical coupling includes an internally-threaded opening that receives a corresponding externally-threaded nipple on the engine block. Oil inlet holes surround the nipple for receiving oil from the engine, and filtered oil is returned to the engine through the nipple. Gaskets surround the inlet holes and the nipple to seal the unit against the engine block. An additional conduit from the filter unit can extend centrally within the nipple to direct oil to a separate part of the vehicle, for example the crankcase. In this case, a filter media with a lower efficiency would typically be used to filter the oil returning to the engine, while a filter media with a higher efficiency would be used to filter the oil returning to the crankcase.
When the filter media becomes clogged with particulate matter and/or contaminants, the flow across the filter media becomes restricted, that is, the pressure on the upstream side of the filter media increases. If the pressure exceeds a predetermined level, more advanced filter units typically include a pressure-sensitive bypass valve which is activated so that the fluid bypasses the filter media and is returned essentially unfiltered to the engine and/or crankcase. In addition, a signalling device is often used to provide an indication to the operator that the filter must be serviced or replaced.
Disposable or throw-away type filter units of the above type are also known in the art. In these units, the entire canister is unscrewed from its threaded connection on the engine block, disposed of, and a new unit is put in its place. This filter unit is relatively expense in that an entirely new unit must be used each time the filter unit is serviced. In addition, the expended unit takes up valuable space in landfills. Karcey; U.S. Pat. No. 4,622,136; and Faria, U.S. Pat. No. 5,066,391, for example, disclose reusable oil filter assemblies wherein a tubular filter element can be removed from the housing, cleaned, and then replaced. The filter element can be accessed through a removable end wall on the canister. The Wilhelm unit, however, has the bypass valve in the head of the filter assembly, which can make it difficult to confirm that the bypass valve is operating properly. On the other hand, in both the Karcey and Faria designs, the filter element is removed by initially removing an end wall and then removing a separate bypass valve. While these reusable units might provide some advantages over the disposable or throw-away type filter units, the reusable units include numerous parts which must be fabricated and kept on hand to manufacture each filter unit, for example separate end walls and bypass valves. Each of these components requires labor and material costs to fabricate and assemble. Further, with these additional components, the complexity of servicing the filter unit is increased.
As such, it is believed that there is a demand in the industry for an improved fluid filter, and in particular, an improved reusable oil filter with a pressure-activated sensing device which provides easy access to the filter elements to facilitate servicing the filter, but which has fewer components to reduce manufacturing costs.